Schlumberger

Case Study: Saltel Expandable Steel Patches Enable High-Rate Fracturing After Casing Damage

Ultraslim patch restores casing mechanical integrity and leaves adequate ID to support fracturing campaign, North Dakota

Challenge: Restore mechanical pressure integrity to damaged casing while minimizing ID restriction to enable high-rate fracturing operations and meet economic goals.

Solution: Install Saltel expandable steel patches to recover mechanical strength while maintaining adequate ID.

Result:

  • Minimized rig time with efficient installations.
  • Passed 9,500-psi [66-MPa] pressure tests.
  • Enabled subsequent high-rate hydraulic fracturing operations.

Casing is damaged during drilling

In preparation for hydraulic fracturing operations, an operator inspected the 7-in, 32-lbm/ft [178-mm, 47.6-kg/m] casing in five wells and found seven weak spots attributed to drilling operations. Although no leaks were detected, logs indicated that the casing thickness remaining in those spots, all at depths from 2,000 to 8,820 ft [610 to 2,690 m], would not support fracturing operations as planned.

To restore the internal pressure rating and integrity of the damaged casing, the operator had a choice between running a fracturing string or tieback system, or setting casing patches. The operator wanted to maintain the ID as much as possible to limit friction losses and thereby ensure that high pump rates could be used as designed for the fracturing operations. However, any solution would have to fit economic criteria as well as technical requirements.

Patch restores casing integrity with maximum ID

Schlumberger recommended the 7-in [178-mm] ultraslim Saltel expandable steel patch, which would leave an ID of 5.69 in [144 mm] after setting. Engineers calculated that each patch, rated to internal service differential pressure of 14,500 psi [100 MPa], would increase the pressure support of the casing by more than 2,500 psi [17 MPa]—adequate to support the planned fracturing operations. Five 13-ft [4-m] patches were selected to cover 1-ft [0.3-m] weak sections and one 36-ft [11-m] patch to cover two weak spots in a single run.

Efficient installation enables high-rate fracturing

Each tubing-conveyed patch was installed in a day and the wells pressure-tested to 9,500 psi [66 MPa]. The customer subsequently performed the high-rate hydraulic fracturing campaign as planned and without incident.


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